1. Field of the Invention
The present invention relates to an image signal processing apparatus, an image pickup apparatus, an image signal processing method and a computer program product. More specifically, the present invention relates to an image signal processing apparatus, an image pickup apparatus, an image signal processing method and a computer program product, which is adapted to perform, by splitting or dividing an image pickup device into more than one section, signal processing on a split or divided section basis, in which a control configuration is included, which is adaptable to eliminate discontinuity of a boundary between split image areas.
2. Description of Related Art
CCDs (Charge Coupled Devices) are widely used as image pickup devices with respect to cameras such as video cameras and still cameras, for instance. In general types of CCDs in related arts, after image pickup information for one frame is detected with a large number of photo detectors (PDs), charge signals resulting from photoelectric conversion are read out through a vertical register and a horizontal register for the sake of conversion into data streams, which are then outputted from one output channel. A CCD of this one-channel output type and its signal processing configuration are described with reference to FIG. 1.
A CCD 10 shown in FIG. 1 has a vertical register 11 for transferring, in a vertical direction, accumulated charges in photo detectors (PDs) as image pickup devices constituting the CCD, a horizontal register 12 for transferring, in a horizontal direction one line at a time, the charges transferred from the vertical register 11, and an output amplifier 13 for converting the charges in the horizontal register 12 into voltage, in which output of the output amplifier 13 is entered into a signal processing unit 21.
The signal processing unit 21 is composed of circuits such as a CDS circuit for performing canceling of noise contained in input signals, an AGC circuit for effecting gain control and an AD converting unit for effecting AD conversion. A digital signal resulting from signal processing in the signal processing unit 21 is once stored in a line memory 22, followed by being outputted through an output unit 23 to provide an output image 30 shown in FIG. 1, for instance.
In recent years, with demands for an increase in signal processing speed and/or in the number of pixels contained in the CCD, there has been proposed one configuration, which performs, by splitting output from the CCD into two or more sections, parallel processing with respect to the split output sections to provide synthesized output. This type of configuration enables faster signal processing to be realized. If two-channel output is given, for instance, it is possible to perform signal processing with respect to output data at an operating frequency as much as a half of an operating frequency for one-channel output.
A two-channel output-adaptive CCD and its signal processing configuration are described with reference to FIG. 2. A CCD 50 shown in FIG. 2 has a vertical register 51 for transferring, in a vertical direction, accumulated charges in photo detectors (PDs) as image pickup devices constituting the CCD, and first and second horizontal registers 52 and 53 for transferring, in a horizontal direction one line at a time, the charges transferred from the vertical register 51. The first horizontal register 52 receives output corresponding to a left half of the photo detectors constituting the CCD, while the second horizontal register 53 receives output corresponding to a right half thereof.
Accumulated data in the first horizontal register 52 is entered into a signal processing unit 61 after the charges are converted into voltage by an output amplifier 54. Accumulated data in the second horizontal register 53 is entered into a signal processing unit 62 after the charges are converted into voltage by an output amplifier 55. The two signal processing units 61 and 62 respectively perform, in parallel, the processing with respect to output data corresponding to the half of the pixels contained in the CCD, the processing of which permits contributions toward realization of high-speed processing.
Data resulting from the signal processing is respectively entered into line memories 63 and 64, and is further synthesized by a multiplexer 65, followed by being outputted through an output unit 66 to provide an output image 70 shown in FIG. 2, for instance.
The configuration shown in FIG. 2 makes it possible to increase an image output speed in such a manner as to perform, by splitting an image pickup area of the CCD into left and right sections, data transfer and signal processing in parallel through the horizontal registers 52 and 53 in the left and the right sections. However, a need exists for use of more than one output amplifiers 54 and 55, causing an output level difference depending on a difference of output amplifier characteristics. Specifically, when with the split CCD output, the split outputs are respectively amplified by the different output amplifiers 54 and 55 as shown in FIG. 2, variations in output data are produced depending on a difference of output amplifier individualities. The output amplifier characteristics depend on manufacturing variations, and it is thus quite difficult to completely match amplifier characteristic values.
The signals having passed through the output amplifiers 54 and 55 are converted into digital signals through the signal processing in the respective signal processing units (blocks of CDS/AGC/AD) 61 and 62, in which case, it is also quite difficult to match CDS/AGC/AD characteristics. As a result, an output image makes an output level difference between left and right images, like the output image 70 shown in FIG. 2.
To make an image pickup area boundary inconspicuous by correcting the difference between the left and the right levels, the output levels of left and right area images have only to be matched. For instance, one technique is included, which is adapted to operate and compare output levels of left and right area images, followed by making correction of one output level so as to match the other. In Japanese Patent Publication No. 3619077 (Patent Document 1), for instance, there is disclosed a level control configuration based on the above technique. However, when applying this technique to the level control configuration, it becomes necessary to make a level comparison after selecting highly correlated pixel areas, or areas having an image of the same subject such as blank areas contained in the left and the right area images, for instance, from pixels of each split area. Accordingly, the processing such as determining of correlativity and selecting of the highly correlated pixel areas is required as for level control. Further, a problem exists that a failure to find any highly correlated pixel area in each split area results in difficulty in carrying out the processing.
In Japanese Patent Application Publication (KOKAI) No. 2002-252808 (patent document 2), there is disclosed a correcting configuration of a type adapted to correct a difference between left and right levels by determining a gain correction value in such a manner as to make leveling of pixel data with respect to left and right channels over more than one line, followed by calculating a difference between the leveled pixel data. However, the configuration of this type also requires the processing with considerations of correlativity between the split areas, resulting in the same problem as the above.
In Japanese Patent Application Publication (KOKAI) No. 2003-143491 (patent document 3), there is disclosed a configuration of a type adapted to make, by installing a control system for independently controlling output from each of left and right channels, adjustment of the control system so as to reduce a level difference. However, the configuration of this type needs to install the control system newly, resulting in a problem of an increase in circuit scale and/or in cost.
In Japanese Patent Application Publication (KOKAI) No. 2004-64404 (patent document 4), there is disclosed a configuration of a type adapted to provide level-controlling data by detecting a level difference between split areas based on image pickup data resulting from image pickup in a light shielded state with an image pickup apparatus, followed by performing level control with respect to the image pickup data. However, the configuration of this type involves a problem of a need for control-parameter acquiring processing before the image pickup.